Not receiving emails

[jeremy14]

Both my iMac and MacBook Pro running Yosemite 10.10.2 are not receiving all the emails being sent to me although my iPad and Dell Windows 7 are receiving them. What could be the problem here?
When I open Mail it can be some hours before the emails arrive all in one slug. Every time I get the triangle with exclamation mark appearing, suggesting that I am disconnected from the internet. Also, I always get the unread emails number showing although I have read every email showing.
All this started after I received Security Update 2015-002 Version 1.0, Installed Mar. 12,2015

Any ideas on why this is happening and what is the solution?

 

[jeremy14]

I didn't get any responses to post above, perhaps because nobody has had this problem. I then contacted my ISP Plus Net who informed me that they had had many subscribers with the same problem and that it was down to the same Security Update 2015-002 Version 1.0, Installed Mar. 12,2015. They then talked me through the fix which went like this.

Go to mail Preferences > Advanced Tab > Check "Use only this server" > TLS Certificate "None".

Voila !! I was in business again.

 

[IWT]

Thank you Jeremy for posting the solution. I couldn't help you as I don't have Yosemite and I don't have the technical knowledge anyway!

Well done you for researching this and finding the answer. Many others may benefit.

Ian